Fuel supply system for internal combustion engine

ABSTRACT

A low-pressure delivery pipe provided with intake manifold injectors, a fuel pressure regulator, a high-pressure fuel pump, a high-pressure delivery pipe provided with in-cylinder injectors, and an electromagnetic relief valve are connected in series at the downstream of a low-pressure fuel pump that discharges a fuel within a fuel tank at a prescribed pressure. Since the low-pressure delivery pipe is arranged downstream of the low-pressure fuel pump, the fuel pressure within the low-pressure delivery pipe is lowered upon stop of vehicle operation, in response to stop of the low-pressure fuel pump. The fuel pressure within the high-pressure delivery pipe is also lowered in response to stop of the low-pressure fuel pump, by opening the electromagnetic relief valve upon stop of vehicle operation. Thus, oil tightness of the injectors during the stop of vehicle operation is ensured.

This nonprovisional application is based on Japanese Patent ApplicationsNos. 2004-197351, 2004-336114 and 2004-362838 filed with the JapanPatent Office on Jul. 2, 2004, Nov. 19, 2004 and Dec. 15, 2004,respectively, the entire contents of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fuel supply system for an internalcombustion engine, and more particularly to a fuel supply system for aninternal combustion engine having first fuel injection means (intakemanifold injector) for injecting a fuel into an intake manifold and/oran intake port, and second fuel injection means (in-cylinder injector)for injecting a fuel into a cylinder.

2. Description of the Background Art

An internal combustion engine provided with an in-cylinder injector(fuel injection valve) for injecting a fuel into a cylinder and anintake manifold injector (fuel injection valve) for injecting a fuelinto an intake port, and controlling the in-cylinder injector and theintake manifold injector in accordance with an operation state to injectthe fuel by combination of intake manifold injection and in-cylinderdirect injection is known (e.g., Japanese Patent Laying-Open No.07-103048).

In a fuel supply system for the internal combustion engine, generally,one fuel line extending from a fuel tank toward the internal combustionengine is branched in the vicinity of the internal combustion engine soas to supply the fuel to an intake manifold injector and to anin-cylinder injector. With this configuration, however, the fuel linehas a complicated configuration in the vicinity of the internalcombustion engine, and the fuel supplied from the fuel tank may besubjected to a great amount of heat from the engine block of theinternal combustion engine. In general, the fuel supplied to the intakemanifold injector is a fuel of a low pressure that is pumped up by usinga low-pressure fuel pump. As such, it has been pointed out that thefuel, when subjected to the great amount of heat from the engine block,may partially vaporize in the fuel line or a delivery pipe for supplyingthe fuel into the intake manifold injector, leading to occurrence ofvapor lock.

To address such a problem, for example, Japanese Patent Laying-Open No.2004-278347 discloses a fuel supply system in which a fuel tank, alow-pressure fuel pump, a fuel pressure regulator (pressure regulator),an intake manifold injection (low-pressure) delivery pipe, ahigh-pressure fuel pump, an in-cylinder injection (high-pressure)delivery pipe, and a relief valve are arranged in series. In this fuelsupply system, it is possible to prevent fuel injection failureattributable to the vapor lock caused in the pipe connected to theintake manifold injector with a simple configuration.

In the fuel supply system for an internal combustion engine as describedabove, it is also necessary to take account of various kinds ofproblems, besides the occurrence of the vapor lock, in association withthe fuel supply to a plurality of systems.

Firstly, it is necessary to achieve a configuration that can improve oiltightness of the injectors during stop of operation of the vehicle, soas to maintain good exhaust property at the time of next start of theengine.

In the fuel supply system disclosed in Japanese Patent Laying-Open No.2004-278347, for example, the intake manifold injection (low-pressure)delivery pipe is arranged downstream of the fuel pressure regulator.Thus, even if an electromagnetic relief valve for releasing pressure isarranged downstream of the in-cylinder injection (high-pressure)delivery pipe, it is difficult to intentionally release the fuelpressure of the low-pressure delivery pipe at the time of stop ofoperation of the vehicle. This leads to poor oil tightness, and theremay occur leakage of the fuel from the intake manifold injector duringstop of operation. Such leakage of the fuel may lead to degradation inexhaust emission property at the time of next start of the engine.

Further, it is necessary to achieve a configuration that enablespreferable fuel injection in accordance with a temperature of theengine.

For example, in a cold state of the engine, atomization of the fuelwithin the cylinder would not be promoted, so that the fuel injectedinto the cylinder tends to adhere to the top face of the engine piston(piston top face) or to the inner peripheral surface of the cylinder(cylinder inner face (bore)) in a large amount. Of the fuel thusadhered, especially the fuel adhered to the piston top face will begradually atomized during the subsequent engine combustion process, anddischarged from the cylinder in the state of imperfect combustion. Thiswill cause generation of black smoke, increase of unburned componentsand the like, leading to degradation of exhaust emission property.Further, the fuel adhered to the cylinder inner face will be mixed withthe lubricant applied to the cylinder inner face for lubrication of theengine piston. This will cause dilution of the lubricant by the fuel,i.e., so-called fuel dilution, so that the lubrication property of theinternal combustion engine may be impaired.

Thus, taking account of the adverse effects of degraded exhaust emissionproperty as well as lowered lubrication property of the internalcombustion engine, it is preferable to inject the fuel from the intakemanifold injector at the time of homogenous combustion operation in thecold state of the engine, while avoiding the fuel injection from thein-cylinder injector.

In the fuel supply system disclosed in Japanese Patent Laying-Open No.2004-278347, however, the intake manifold injection delivery pipe andthe in-cylinder injection delivery pipe are connected in series, withthe intake manifold injection delivery pipe located upstream of thein-cylinder injection delivery pipe. As such, in the cold state of theengine, the temperature increase of the fuel within the in-cylinderinjection delivery pipe is slow, and the atomized particle size of thefuel injected from the intake manifold injector tends to become large,leading to degradation of exhaust emission property.

Meanwhile, when the operation of the internal combustion engine proceeds(i.e., in the warm state of the engine), the temperature at the tip endof the in-cylinder injector increases with the fuel combustion withinthe combustion chamber, and deposits tend to be produced in theinjection hole at the tip of the in-cylinder injector, which cools thein-cylinder injector. Therefore, it is preferable that the fueltemperature within the in-cylinder injection delivery pipe is low.

With the configuration disclosed in Japanese Patent Laying-Open No.2004-278347, however, the in-cylinder injection delivery pipe isarranged downstream. Thus, only the fuel of the quantity correspondingto the overall fuel quantity supplied from the fuel pump from which thefuel quantity injected from the intake manifold injector is subtracted,is applied with pressure by using the high-pressure fuel pump andprovided to the in-cylinder injection delivery pipe. That is, since thefuel flow rate within the in-cylinder injection delivery pipe is small,the fuel temperature within the in-cylinder injection delivery pipetends to increase due to the heat received from the internal combustionengine. As such, the effect of cooling the in-cylinder injector is notobtained sufficiently, which is disadvantageous in view of accumulationof deposits.

Still further, since there exist a plurality of fuel systems (of highpressure and of low pressure), it is also necessary to achieve aconfiguration that can prevent vapor lock within the fuel supply systemattributable to the difference in fuel injection quantity between thefuel systems.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above-describedproblems. A first object of the present invention is to provide a fuelsupply system for an internal combustion engine provided with a firstfuel injection unit (intake manifold injector) for injecting a fuel intoan intake manifold and/or an intake port and a second fuel injectionunit (in-cylinder injector) for injecting a fuel into a cylinder, thatcan improve oil tightness of the injectors during stop of operation ofthe vehicle and that can maintain good exhaust emission property at thetime of start of the engine.

A second object of the present invention is to provide a fuel supplysystem for an internal combustion engine provided with a first fuelinjection unit (intake manifold injector) for injecting a fuel into anintake manifold and/or an intake port and a second fuel injection unit(in-cylinder injector) for injecting a fuel into a cylinder, that canimprove exhaust emission property at the time of intake manifoldinjection in a cold state of the engine and that can suppress productionof deposits at the tip end of the in-cylinder injector.

A third object of the present invention is to provide a fuel supplysystem for an internal combustion engine that can suppress generation ofvapor lock attributable to insufficient fuel supply quantity to ahigh-pressure fuel pump.

A fuel supply system for an internal combustion engine according to thepresent invention includes a fuel tank, a first fuel pump, a first fueldelivery pipe, a second fuel pump, a second fuel delivery pipe, apressure regulation unit, and a pressure release unit. The fuel tankstores a fuel. The first fuel pump is actuated in response to anoperation instruction associated with an operation period of theinternal combustion engine and discharges the fuel in the fuel tank at afirst pressure. The first fuel delivery pipe is formed as a tubular bodyhaving a first fuel injection unit, receives the fuel discharged fromthe first fuel pump at an upstream side, and delivers the fuel to thefirst fuel injection unit such that the fuel is injected into theinternal combustion engine. The second fuel pump is connected in serieswith the first fuel delivery pipe, is actuated during operation of theinternal combustion engine, and applies pressure to the fuel receivedfrom a downstream side of the first fuel delivery pipe to discharge thefuel at a second pressure. The second fuel delivery pipe is formed as atubular body having a second fuel injection means, receives the fueldischarged from the second fuel pump at an upstream side, and deliversthe fuel to the second fuel injection unit such that the fuel isinjected into the internal combustion engine. The pressure regulationunit is provided on a fuel path between the first fuel delivery pipe andthe second fuel pump, and guides the fuel in the fuel path to a pressurerelease path when a pressure of the fuel in the fuel path exceeds thefirst pressure. The pressure release unit is provided between the fuelpath downstream of the second fuel pump and the pressure release path,and is actuated at the stop of operation of a vehicle to guide the fuelin the fuel path to the pressure release path.

According to this fuel supply system for an internal combustion engine,in the configuration where the first and second fuel injection units areprovided independently from each other, the first fuel delivery pipe(low-pressure delivery pipe) is arranged upstream of the pressureregulation unit (fuel pressure regulator). Thus, at the end of operationof the vehicle (i.e., at the stop of operation of the internalcombustion engine), the fuel pressure in the first fuel delivery pipecan be lowered in response to stop of the first fuel pump (low-pressurefuel pump), and the fuel pressure in the second fuel delivery pipe(high-pressure delivery pipe) can also be lowered by activating thepressure release unit. This can prevent degradation in oil tightness ofthe first fuel injection unit (intake manifold injector) and the secondfuel injection unit (in-cylinder injector) during the time period wherethe operation is stopped until the next start of operation, and thus,leakage of the fuel from the fuel injection units, and hence,degradation in exhaust property at the next start of the internalcombustion engine can be prevented. Further, since the fuel dischargedfrom the first fuel pump is guided through the first fuel delivery pipe,the pressure regulation unit, the second fuel pump (high-pressure pump)and the second fuel delivery pipe connected in series, fuel injectionfailure attributable to vapor lock generated in the pipe of thelow-pressure system is avoided with a simple configuration.

A fuel supply system for an internal combustion engine according toanother configuration of the present invention includes a fuel tank, afirst fuel pump, a first fuel delivery pipe, a pressure regulation unit,a second fuel pump, a second fuel delivery pipe, a first pressurerelease unit, and a second pressure release unit. The fuel tank stores afuel. The first fuel pump is actuated in response to an operationinstruction associated with an operation period of the internalcombustion engine, and discharges the fuel in the fuel tank at a firstpressure. The first fuel delivery pipe is formed as a tubular bodyhaving a first fuel injection unit, receives the fuel discharged fromthe first fuel pump at an upstream side, and delivers the fuel to thefirst fuel injection unit such that the fuel is injected into theinternal combustion engine. The pressure regulation unit is provided ona fuel path between the first fuel pump and an upstream side of thefirst fuel delivery pipe, and guides the fuel in the fuel path to apressure release path when a pressure of the fuel in the fuel pathexceeds the first pressure. The second fuel pump is actuated duringoperation of the internal combustion engine, receives the fuel outputfrom the first fuel pump, and further applies pressure to the fuel todischarge the fuel at a second pressure. The second fuel delivery pipeis formed as a tubular body having a second fuel injection unit,receives the fuel discharged from the second fuel pump, and delivers thefuel to the second fuel injection unit such that the fuel is injectedinto the internal combustion engine. The first pressure release unit isprovided on a fuel path between the pressure regulation unit and thefirst fuel delivery pipe, and is activated at the stop of operation of avehicle to guide the fuel in the fuel path to a pressure release path.The second pressure release unit is provided on a fuel path downstreamof the second fuel pump, and is activated at the stop of the operationof the vehicle to guide the fuel in the fuel path to a pressure releasepath.

According to this fuel supply system for an internal combustion engine,in the configuration where the first and second fuel injection units areprovided independently from each other, the first and second pressurerelease units are activated at the end of operation of the vehicle(i.e., at the stop of operation of the internal combustion engine), andthus, the fuel pressures in the first fuel delivery pipe (low-pressuredelivery pipe) and in the second fuel delivery pipe (high-pressuredelivery pipe) can be lowered. This can prevent degradation in oiltightness of the first fuel injection unit (intake manifold injector)and the second fuel injection unit (in-cylinder injector) during thetime period where the operation is stopped until the next start ofoperation, and thus, leakage of the fuel from the fuel injection unitsis prevented. Accordingly, degradation in exhaust emission property atthe next start of the internal combustion engine can be prevented.

The first fuel pump is activated in response to an operation instructionassociated with an operation period of the internal combustion engine.Thus, for example by generating the operation instruction in response toan operation start instruction of the internal combustion engine, it ispossible to make the first fuel pump enter an operating state before theinternal combustion engine actually starts operation.

Preferably, in the fuel supply system for an internal combustion engineaccording to the other configuration, the pressure regulation unit isintegrally provided in the fuel tank.

According to this configuration, the pressure regulation unit can bearranged occupying only a small area.

Still preferably, the pressure release path is a fuel return pipe to thefuel tank.

Still preferably, in the fuel supply system for an internal combustionengine of the present invention, the first fuel injection unit (intakemanifold injector) injects the fuel into an intake manifold of theinternal combustion engine, and the second fuel injection unit(in-cylinder injector) injects the fuel into a combustion chamber of theinternal combustion engine.

According to this fuel supply system for an internal combustion engine,where fuel injection into an intake manifold and fuel injection into acombustion chamber can be carried out independently from each other,degradation in oil tightness of the fuel injection units can beprevented as described above, and thus, degradation in exhaust propertyat the start of operation of the internal combustion engine can also beprevented.

A fuel supply system for an internal combustion engine according to yetanother configuration of the present invention is provided with a firstfuel injection unit for injecting a fuel into an intake manifold and asecond fuel injection unit for injecting a fuel into a cylinder, andincludes a first fuel delivery pipe, a fuel pump, and a second fueldelivery pipe. The first fuel delivery pipe delivers the fuel receivedat an upstream side to the first fuel injection unit such that the fuelis injected into the intake manifold. The fuel pump discharges a fuel ina fuel tank at a prescribed pressure. The second fuel delivery pipereceives the fuel discharged by the fuel pump at an upstream side anddelivers the fuel to the second fuel injection unit such that the fuelis injected into the cylinder. The first and second fuel delivery pipesare connected in series, with the upstream side of the first fueldelivery pipe being connected to a downstream side of the second fueldelivery pipe.

According to this fuel supply system for an internal combustion engine,the first fuel delivery pipe for intake manifold injection and thesecond fuel delivery pipe for in-cylinder fuel injection are connectedin series. This can simplify the system configuration, as the branchedfuel paths are necessary. Further, it can be configured such that thefuel to be injected from the first fuel injection unit (intake manifoldinjector) is supplied to the first fuel delivery pipe (PFI deliverypipe) after being passed through the second fuel delivery pipe (DIdelivery pipe).

Thus, compared to the configuration where the first fuel delivery pipeis arranged upstream, the temperature of the fuel injected from thefirst fuel injection unit in a cold state of the engine can be increasedquickly. Accordingly, in the cold start of the engine where it ispreferable to avoid fuel injection from the second fuel injection unit(in-cylinder injector), the atomized particle size of the fuel injectedfrom the first fuel injection unit can be downsized, so that thedegradation of exhaust emission property can be prevented.

Further, compared to the configuration where the first fuel deliverypipe is arranged upstream, the flow rate of the fuel in the second fueldelivery pipe is large, and thus, during the warm state of the engine,the temperature increase of the fuel within the second fuel deliverypipe along with the operation of the internal combustion engine issuppressed. As a result, the cooling effect of the second fuel injectionunit by the fuel passing through the second fuel delivery pipe or by thefuel injected therefrom is ensured, and accordingly, the temperatureincrease of the second fuel injection unit conducting in-cylinderinjection is suppressed, and production of deposits is prevented.

Preferably, in the fuel supply system for an internal combustion engine,the second fuel delivery pipe is arranged at a position receiving heatfrom the internal combustion engine.

According to this fuel supply system for an internal combustion engine,the fuel to be injected from the first and second fuel injection unitsis passed through the second fuel delivery pipe subjected to a greatamount of heat. This further improves the exhaust property in the coldstate of the engine, and also considerably improves the effect ofpreventing production of deposits in the second fuel injection unitalong with the operation of the internal combustion engine.

Preferably, the fuel supply system for an internal combustion enginefurther includes a first fuel pressure regulation unit and a second fuelpressure regulation unit. The fuel pump discharges the fuel at a firstprescribed pressure. The first fuel pressure regulation unit is arrangeddownstream of the second fuel delivery pipe and maintains a pressure ofthe fuel in the second fuel delivery pipe at the first prescribedpressure. The second fuel pressure regulation unit is arrangeddownstream of the first fuel delivery pipe and maintains a pressure ofthe fuel in the first fuel delivery pipe at a second prescribed pressurelower than the first prescribed pressure.

According to this fuel supply system for an internal combustion engine,the fuel injection pressure from the second fuel injection unitconducting direct in-cylinder injection is set at a high pressurerequired for atomization of the fuel, while the fuel injection pressurefrom the first fuel injection unit conducting intake manifold injectionis set at a low pressure. Accordingly, the designed withstand pressureof the first fuel injection unit and the first fuel delivery pipe notrequiring fuel atomization with the high pressure can be lowered, whichleads to reduction of the manufacturing cost.

More preferably, in the fuel supply system for an internal combustionengine, the first fuel pressure regulation unit is a relief valve thatopens when a pressure larger than the first prescribed pressure isapplied from the fuel and can open in response to an electric signal.

According to this fuel supply system for an internal combustion engine,the relief valve is opened at the stop of operation, for example, so asto form a pressure release path at the downstream side of the secondfuel delivery pipe as well as at the upstream side of the first fueldelivery pipe. Thus, it is possible to sufficiently lower the fuelpressure within the first and second fuel delivery pipes during the stopof operation of the internal combustion engine, and oil tightness of thefirst and second fuel injection units is improved. As a result, it ispossible to suppress degradation of exhaust emission property at thenext start of the internal combustion engine.

Alternatively, the fuel supply system for an internal combustion enginefurther includes a fuel pressure regulation unit. The fuel pressureregulation unit is arranged downstream of the first fuel delivery pipe,and guides the fuel to a pressure release path when a prescribedpressure is applied from the fuel. The pressure of the fuel injectedfrom the first fuel injection unit and the pressure of the fuel injectedfrom the second fuel injection unit are substantially equal.

According to this fuel supply system for an internal combustion engine,the fuel injection pressure of the first fuel injection unit conductingintake manifold fuel injection and the fuel injection pressure of thesecond fuel injection unit conducting direct in-cylinder fuel injectionare equal. Specifically, they are set to a high pressure required foratomization of the fuel injected into the cylinder. Since the fuelpressure within the fuel supply system becomes constant, the systemconfiguration is simplified, and the atomized particle size of the fuelinjected from the first fuel injection unit is further downsized.Accordingly, the exhaust emission property in the cold state of theengine is further improved.

Still preferably, in the fuel supply system for an internal combustionengine, the fuel pressure regulation unit is a relief valve that openswhen the prescribed pressure is applied from the fuel and can open inresponse to an electric signal.

According to this fuel supply system for an internal combustion engine,the pressure release path is formed downstream of the first fueldelivery pipe by opening the relief valve at the stop of operation, forexample. This can lower the fuel pressure within the first and secondfuel delivery pipes. Accordingly, oil tightness in the first and secondfuel injection units during the stop of operation of the internalcombustion engine is improved, and degradation in exhaust emissionproperty at the next start of operation of the internal combustionengine is prevented.

A fuel supply system for an internal combustion engine according to yetanother configuration of the present invention has an in-cylinderinjector provided at an in-cylinder injection fuel delivery pipe and forinjecting a fuel into a combustion chamber and an intake manifoldinjector provided at an intake manifold injection fuel delivery pipe andfor injecting a fuel into an intake manifold, and applies pressure to afuel discharged from a low-pressure fuel pump by using a high-pressurefuel pump to supply the fuel to the in-cylinder injection fuel deliverypipe. The fuel supply system includes a connection fuel pipe connectinga downstream side of the high-pressure fuel pump to an upstream side ofthe intake manifold injection fuel delivery pipe, and an intake manifoldinjection pressure regulation unit for adjusting a pressure of the fuelwithin the intake manifold injection fuel delivery pipe.

According to this fuel supply system for an internal combustion engine,all of the fuel discharged from the low-pressure fuel pump is suppliedto the high-pressure fuel pump. This advantageously prevents generationof vapor lock attributable to insufficient fuel supply from thelow-pressure fuel pump to the high-pressure fuel pump.

Generally, in the case where the downstream side of the high-pressurefuel pump is connected to the upstream side of the intake manifoldinjection fuel delivery pipe and pressure regulation is not performedfor the fuel within the intake manifold injection fuel delivery pipe,the fuel of the high pressure discharged from the high-pressure fuelpump is flown into the intake manifold injection fuel delivery pipe,making it difficult to accurately conduct the fuel injection from theintake manifold injector.

By comparison, according to the above fuel supply system for an internalcombustion engine, the intake injection pressure regulation unitregulates the pressure of the fuel within the intake manifold injectionfuel delivery pipe, and accordingly, the fuel injection from the intakemanifold injector can be carried out with accuracy.

Alternatively, a fuel supply system for an internal combustion engineaccording to yet another configuration of the present inventionincludes: an in-cylinder injector for injecting a fuel into a combustionchamber; an in-cylinder injection fuel delivery pipe provided with thein-cylinder fuel injector; a low-pressure fuel pump for pumping up afuel from a fuel tank; a fuel supply pipe for connecting a dischargeport of the low-pressure fuel pump to an upstream side of thein-cylinder injection fuel delivery pipe; a high-pressure fuel pump forapplying pressure to the fuel discharged from the low-pressure fuel pumpand supplying the fuel to the in-cylinder injection fuel delivery pipe;an in-cylinder injection pressure regulation valve provided at the fuelsupply pipe downstream of the high-pressure fuel pump and for regulatinga pressure of the fuel within the in-cylinder injection fuel deliverypipe not to exceed an in-cylinder injection pressure; an intake manifoldinjector for injecting a fuel into an intake manifold; an intakemanifold injection fuel delivery pipe provided with the intake manifoldinjector; a connection fuel pipe for connecting an outlet port of thein-cylinder injection pressure regulation valve to an upstream side ofthe intake manifold injection fuel delivery pipe; a fuel return pipe forconnecting a downstream side of the intake manifold injection fueldelivery pipe to the fuel tank; and an intake manifold injectionpressure regulation valve provided at the fuel return pipe and forregulating a pressure of the fuel within the intake manifold injectionfuel delivery pipe not to exceed an intake manifold injection pressurethat is lower than the in-cylinder injection pressure.

With this configuration as well, the effects similar to those achievedby the above fuel supply system can be obtained.

Still alternatively, a fuel supply system for an internal combustionengine according to yet another configuration of the present inventionincludes: an in-cylinder injector for injecting a fuel into a combustionchamber; an in-cylinder injection fuel delivery pipe provided with thein-cylinder injector; a low-pressure fuel pump for pumping up a fuelfrom a fuel tank; a fuel supply pipe for connecting a discharge port ofthe low-pressure fuel pump to an upstream side of the in-cylinderinjection fuel delivery pipe; a high-pressure fuel pump for applyingpressure to the fuel discharged from the low-pressure fuel pump and forsupplying the fuel to the in-cylinder injection fuel delivery pipe; anintake manifold injector for injecting a fuel into an intake manifold;an intake manifold injection fuel delivery pipe provided with the intakemanifold injector; a connection fuel pipe for connecting a downstreamside of the in-cylinder injection fuel delivery pipe to an upstream sideof the intake manifold injection fuel delivery pipe; an in-cylinderinjection pressure regulation valve provided at the connection fuel pipeand for regulating a pressure of the fuel within the in-cylinderinjection fuel delivery pipe not to exceed an in-cylinder injectionpressure; a fuel return pipe for connecting a downstream side of theintake manifold injection fuel delivery pipe to the fuel tank; and anintake manifold injection pressure regulation valve provided at the fuelreturn pipe and for regulating a pressure of the fuel within the intakemanifold injection fuel delivery pipe not to exceed an intake manifoldinjection pressure that is lower than the in-cylinder injectionpressure.

With this configuration as well, the effects similar to those achievedby the above fuel supply system can be obtained.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram of an engine system to whicha fuel supply system according to a first embodiment of the presentinvention is applied.

FIG. 2 illustrates in detail a configuration of the fuel supply systemof FIG. 1.

FIG. 3 is a timing diagram illustrating operation timings of alow-pressure fuel pump and pressure release means (electromagneticrelief valve) in the fuel supply system according to the firstembodiment.

FIG. 4 illustrates a configuration example of a fuel supply system foran internal combustion engine according to a modification of the firstembodiment.

FIG. 5 is a timing diagram illustrating operation timings of alow-pressure fuel pump and pressure release means (electromagneticrelief valve) in the fuel supply system shown in FIG. 4.

FIG. 6 is a schematic configuration diagram of an engine systemincorporating a fuel supply system for an internal combustion engineaccording to a second embodiment of the present invention.

FIG. 7 is a configuration diagram of the fuel supply system for aninternal combustion engine according to the second embodiment.

FIG. 8 is a configuration diagram showing another example of the fuelsupply system for an internal combustion engine according to the secondembodiment.

FIG. 9 is a configuration diagram of a fuel supply system for aninternal combustion engine according to a modification of the secondembodiment.

FIG. 10 is a configuration diagram showing another example of the fuelsupply system for an internal combustion engine according to themodification of the second embodiment.

FIG. 11 is a diagram showing a cross-sectional structure of an engine towhich a fuel supply system according to the present invention isapplied.

FIG. 12 is a configuration diagram of a fuel supply system for aninternal combustion engine according to a third embodiment of thepresent invention.

FIG. 13 illustrates the flow of the fuel in the fuel supply system shownin FIG. 12.

FIG. 14 is a configuration diagram of a fuel supply system for aninternal combustion engine according to a modification of the thirdembodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the drawings.

First Embodiment

FIG. 1 schematically shows an engine system incorporating a fuel supplysystem for an internal combustion engine according to a first embodimentof the present invention. Although an in-line 4-cylinder gasoline engineis shown in FIG. 1, application of the present invention is notrestricted to the engine shown.

As shown in FIG. 1, the engine (internal combustion engine) 10 includesfour cylinders 112, which are connected via corresponding intakemanifolds 20 to a common surge tank 30. Surge tank 30 is connected viaan intake duct 40 to an air cleaner 50. In intake duct 40, an airflowmeter 42 and a throttle valve 70, which is driven by an electric motor60, are disposed. Throttle valve 70 has its degree of opening controlledbased on an output signal of an engine ECU (Electronic Control Unit)300, independently from an accelerator pedal 100. Cylinders 112 areconnected to a common exhaust manifold 80, which is in turn connected toa three-way catalytic converter 90.

For each cylinder 112, an in-cylinder injector 110 for injecting a fuelinto the cylinder and an intake manifold injector 120 for injecting afuel into an intake port and/or an intake manifold are provided.

Injectors 110, 120 are controlled based on output signals of engine ECU300. In-cylinder injectors 110 are connected to a common fuel deliverypipe (also referred to as “high-pressure delivery pipe” in the firstembodiment) 130, and intake manifold injectors 120 are connected to acommon fuel delivery pipe (also referred to as “low-pressure deliverypipe” in the first embodiment) 160. Fuel supply to fuel delivery pipes130, 160 is carried out by a fuel supply system 150, which will bedescribed later in detail.

Engine ECU 300 is configured with a digital computer, which includes aROM (Read Only Memory) 320, a RAM (Random Access Memory) 330, a CPU(Central Processing Unit) 340, an input port 350, and an output port360, which are connected to each other via a bidirectional bus 310.

Airflow meter 42 generates an output voltage that is proportional to anintake air amount, and the output voltage of airflow meter 42 is inputvia an A/D converter 370 to input port 350. A coolant temperature sensor380 is attached to engine 10, which generates an output voltageproportional to an engine coolant temperature. The output voltage ofcoolant temperature sensor 380 is input via an A/D converter 390 toinput port 350.

A fuel pressure sensor 400 is attached to high-pressure delivery pipe130, which generates an output voltage proportional to a fuel pressurein high-pressure delivery pipe 130. The output voltage of fuel pressuresensor 400 is input via an A/D converter 410 to input port 350. Anair-fuel ratio sensor 420 is attached to exhaust manifold 80 locatedupstream of three-way catalytic converter 90. Air-fuel ratio sensor 420generates an output voltage proportional to an oxygen concentration inthe exhaust gas, and the output voltage of air-fuel ratio sensor 420 isinput via an A/D converter 430 to input port 350.

Air-fuel ratio sensor 420 in the engine system of the present embodimentis a full-range air-fuel ratio sensor (linear air-fuel ratio sensor)that generates an output voltage proportional to an air-fuel ratio ofthe air-fuel mixture burned in engine 10. As air-fuel ratio sensor 420,an O₂ sensor may be used which detects, in an on/off manner, whether theair-fuel ratio of the mixture burned in engine 10 is rich or lean withrespect to a theoretical air-fuel ratio.

Accelerator pedal 100 is connected to an accelerator press-down degreesensor 440 that generates an output voltage proportional to the degreeof press-down of accelerator pedal 100. The output voltage ofaccelerator press-down degree sensor 440 is input via an A/D converter450 to input port 350. An engine speed sensor 460 generating an outputpulse representing the engine speed is connected to input port 350. ROM320 of engine ECU 300 prestores, in the form of a map, values of fuelinjection quantity that are set corresponding to operation states basedon the engine load factor and the engine speed obtained by theabove-described accelerator press-down degree sensor 440 and enginespeed sensor 460, respectively, and the correction values based on theengine coolant temperature.

Engine ECU 300 generates various control signals for controlling theoverall operations of the engine system based on signals from therespective sensors by executing a prescribed program. The controlsignals are transmitted to the devices and circuits constituting theengine system via an output port 360 and drive circuits 470.

FIG. 2 illustrates in detail the configuration of fuel supply system 150shown in FIG. 1.

In FIG. 2, the portions other than in-cylinder injectors 110,high-pressure delivery pipe 130, intake manifold injectors 120 andlow-pressure delivery pipe 160 correspond to the fuel supply system 150of FIG. 1.

The fuel stored in a fuel tank 200 is discharged at a prescribedpressure by a low-pressure fuel pump 180 of an electric motor-driventype. Low-pressure fuel pump 180 is controlled based on a control signalfrom an ECU 300#. Here, ECU 300# corresponds to a functional part ofengine ECU 300 of FIG. 1 that is related to control of the fuel supplysystem.

The discharge side of low-pressure fuel pump 180 is connected via a fuelfilter 190 and a fuel pipe 135 to a low-pressure delivery pipe 160 thatis formed as a tubular body provided with intake manifold injectors 120.That is, low-pressure delivery pipe 160 receives the fuel dischargedfrom low-pressure fuel pump 180 via fuel pipe 135 on the upstream side,and delivers the fuel to intake manifold injectors 120 so as to beinjected into the internal combustion engine. It is noted that in theapplication of the present invention, an arbitrary number of (i.e., oneor more) intake manifold injectors 120 may be provided to low-pressuredelivery pipe 160.

The downstream side of low-pressure delivery pipe 160 is connected tothe intake side of a high-pressure fuel pump 155 of an engine-driventype. Fuel pressure regulator 170 is configured to guide the fuel on thedownstream side of low-pressure delivery pipe 160 to a fuel return pipe220 when a pressure (fuel pressure) of the fuel becomes higher than apreset pressure. As such, the fuel pressure on the downstream side offuel pressure regulator 170 is maintained so as not to exceed the presetpressure.

The discharge side of high-pressure fuel pump 155 is connected to a fuelpipe 165 via a check valve 140 that allows the flow toward the fuel pipe165. Fuel pipe 165 is connected to a high-pressure delivery pipe 130that is formed as a tubular body provided with in-cylinder injectors110. It is also noted that an arbitrary number of (i.e., one or more)in-cylinder injectors 110 may be provided to high-pressure delivery pipe130.

The discharge side of high-pressure fuel pump 155 is also connected tothe intake side of high-pressure fuel pump 155 via an electromagneticspill valve 156. As the degree of opening of electromagnetic spill valve156 decreases, the quantity of the fuel supplied from high-pressure fuelpump 155 to fuel pipe 165 increases. When electromagnetic spill valve156 is fully open, fuel supply from high-pressure pump 155 to fuel pipe165 is stopped. Electromagnetic spill valve 156 is controlled inresponse to an output signal of ECU 300#.

High-pressure delivery pipe 130 receives on its upstream side the fueldischarged from high-pressure fuel pump 155 via fuel pipe 165, anddelivers the fuel to in-cylinder injectors 110 so as to be injected intothe internal combustion engine. Further, an electromagnetic relief valve210 is provided on the downstream side of high-pressure delivery pipe130. Electromagnetic relief valve 210 is opened in response to a controlsignal from ECU 300#, and guides the fuel within high-pressure deliverypipe 130 to fuel return pipe 220.

As such, in the fuel supply system according to the present embodiment,low-pressure delivery pipe 160 and high-pressure delivery pipe 130 arearranged in series, as in Japanese Patent Laying-Open No. 2004-278347described above, and then low-pressure delivery pipe 160 is arrangedupstream of fuel pressure regulator 170.

In the fuel supply system shown in FIG. 2, low-pressure fuel pump 180and low-pressure delivery pipe 160 correspond to the “first fuel pump”and the “first fuel delivery pipe”, respectively, of the presentinvention. High-pressure fuel pump 155 and high-pressure delivery pipe130 correspond to the “second fuel pump” and the “second fuel deliverypipe”, respectively, of the present invention. Further, fuel pressureregulator 170 corresponds to the “pressure regulation unit”, fuel returnpipe 220 corresponds to the “pressure release path”, and electromagneticrelief valve 210 corresponds to the “pressure release means” of thepresent invention.

Hereinafter, operation timings of the low-pressure fuel pump and thepressure release means (electromagnetic valve) in the fuel supply systemaccording to the first embodiment of the present invention will bedescribed with reference to FIG. 3.

Referring to FIG. 3, operation of low-pressure fuel pump 180 iscontrolled in accordance with a control signal (“LOW-PRESSURE FUEL PUMPCONTROL SIGNAL” in FIG. 3) from engine ECU 300 that corresponds to theoperation period of engine 10. As such, at the start of operation of thevehicle, electromagnetic relief valve 210 is switched from the openstate to the closed state, and the operation of low-pressure fuel pump180 is also started.

Further, in response to activation of the starter, engine 10 isactivated to enter an operating state. That is, the operations oflow-pressure fuel pump 180 and electromagnetic relief valve 210 arecontrolled using the start of operation as a trigger, so that it isensured that the fuel pressure in the low-pressure system is increasedby driving low-pressure fuel pump 180 and electromagnetic relief valve210 is closed at the timing of start of engine 10.

High-pressure fuel pump 155 also starts operation in accordance with thestart of engine 10, and fuel injection from the high-pressure system(in-cylinder injectors 110) becomes possible in addition to fuelinjection from the low-pressure system (intake manifold injectors 120).

At the end of operation of the vehicle, the operation of low-pressurefuel pump 180 is stopped in response to stop of engine 10, andelectromagnetic relief valve 210 is opened. For example, the start andend of the operation correspond to on and off of the ignition switch.

Referring again to FIG. 2, as electromagnetic relief valve 210 is openedat the end of operation, the fuel pressure in high-pressure deliverypipe 130 is sufficiently lowered. Further, since low-pressure deliverypipe 160 is arranged upstream of fuel pressure regulator 170, the fuelpressure within low-pressure delivery pipe 160 can be lowered inresponse to stop of low-pressure fuel pump 180.

As such, during the time period in which operation is stopped until thenext start of operation, oil tightness of high-pressure delivery pipe130 and low-pressure delivery pipe 160 will not be degraded, and thus,the leakage of the fuel from in-cylinder injectors 110 and intakemanifold injectors 120 is prevented. Accordingly, it is possible toprevent degradation in exhaust emission property at the time of enginestart upon the next start of operation.

Further, in the fuel supply system shown in FIG. 2, as in the case ofJapanese Patent Laying-Open No. 2004-278347, the fuel discharged fromlow-pressure fuel pump 180 is guided through low-pressure delivery pipe160, fuel pressure regulator 170, high-pressure fuel pump 155 andhigh-pressure delivery pipe 130 connected in series. Thus, it ispossible with a simple configuration to prevent fuel injection failureattributable to the vapor lock generated within the pipe of thelow-pressure system connected to the intake manifold injectors.

Modification of First Embodiment

A configuration example of a fuel supply system for an internalcombustion engine according to a modification of the first embodimentwill now be explained.

Referring to FIG. 4, the fuel supply system according to themodification of the first embodiment differs from the configurationexample shown in FIG. 2 in that the fuel discharged from low-pressurefuel pump 180 and passed through fuel pressure regulator 170 is guidedto branched paths of one directed to low-pressure delivery pipe 160 andthe other directed to high-pressure delivery pipe 130.

The fuel discharged from low-pressure fuel pump 180 of the electricmotor-driven type is supplied via fuel filter 190 to fuel pressureregulator 170. Fuel pressure regulator 170 is arranged upstream oflow-pressure delivery pipe 160, and is configured to return a part ofthe fuel discharged from low-pressure fuel pump 180 back to fuel tank200 when the fuel pressure of the discharged fuel becomes greater than apreset fuel pressure. This ensures that the fuel pressure on thedownstream side of fuel pressure regulator 170 is maintained at thepreset fuel pressure or lower.

On the downstream side of fuel pressure regulator 170, branched fuelpipes 135 and 136 are provided.

The fuel discharged from low-pressure fuel pump 180 and passed throughfuel pressure regulator 170 is delivered via fuel pipe 135 tolow-pressure delivery pipe 160. An electromagnetic relief valve 205 isprovided in a fuel path extending from fuel pressure regulator 170 tolow-pressure delivery pipe 160, at a certain position of fuel pipe 135.

When the fuel pressure in fuel pipe 135 becomes greater than aprescribed pressure, electromagnetic relief valve 205 forms a path forguiding a part of the fuel to fuel return pipe 220 so as to lower thefuel pressure in low-pressure delivery pipe 160 and fuel pipe 135. Inaddition, electromagnetic relief valve 205 is forcibly opened inresponse to a control signal from ECU 300# to form a path extending fromfuel pipe 135 to fuel return pipe 220.

Fuel pipe 136 is connected to the intake side of high-pressure fuel pump155. An electromagnetic spill valve 156 is provided on the dischargeside of high-pressure fuel pump 155. The discharge side of high-pressurefuel pump 155 is connected via fuel pipe 165 to high-pressure deliverypipe 130.

Further, on the downstream side of high-pressure delivery pipe 130, anelectromagnetic relief valve 210 is arranged between the pipe 130 andfuel return pipe 220, as in the case of the configuration example ofFIG. 2.

In the fuel supply system of FIG. 4, electromagnetic relief valve 205corresponds to the “first pressure release means” of the presentinvention, and electromagnetic relief valve 210 corresponds to the“second pressure release means” of the present invention.

FIG. 5 illustrates operations of the electromagnetic relief valves andthe low-pressure fuel pump in the fuel supply system for an internalcombustion engine shown in FIG. 4.

Referring to FIG. 5, the operation of low-pressure fuel pump 180 iscontrolled in accordance with a control signal (“LOW-PRESSURE FUEL PUMPCONTROL SIGNAL”) associated with the operation period of engine 10, asin the case of FIG. 3.

Electromagnetic relief valves 205 and 210 are controlled in the samemanner as electromagnetic relief valve 210 in FIG. 3, i.e., closed inresponse to the start of operation of the vehicle and opened in responseto the end of operation of the vehicle.

Accordingly, in the fuel supply system shown in FIG. 4, the fuelpressure in high-pressure delivery pipe 130 can be lowered by openingelectromagnetic relief valve 210 at the end of operation of the vehicle,and the fuel pressure in low-pressure delivery pipe 160 arrangeddownstream of fuel pressure regulator 170 can also be loweredsufficiently by opening electromagnetic relief valve 205. In thismanner, as in the case of the fuel supply system shown in FIG. 2,leakage of the fuel from in-cylinder injectors 110 and intake manifoldinjectors 120 during the stop of operation of the vehicle is prevented,and thus, degradation in exhaust property at the engine start upon nextstart of operation can be prevented.

Although the configuration of guiding the fuel to fuel return pipe 220at the opening of electromagnetic relief valves (pressure release means)205, 210 has been described in the first embodiment and its modification(FIGS. 2 and 4), each valve may be configured to guide the fuel toanother location in the fuel supply system as long as it can lower thefuel pressure within the corresponding delivery pipe.

Second Embodiment

FIG. 6 schematically shows an engine system incorporating a fuel supplysystem for an internal combustion engine according to a secondembodiment of the present invention.

In the engine system shown in FIG. 6, a fuel supply system 500 of thesecond embodiment is provided in place of fuel supply system 150 inFIG. 1. The fuel supply to fuel delivery pipes 130 and 160 is carriedout by fuel supply system 500.

In the second embodiment, fuel delivery pipe 130 connected within-cylinder injector 110 is also referred to as “DI delivery pipe”, andfuel delivery pipe 160 connected with intake manifold injector 120 isalso referred to as “PFI delivery pipe”.

The other portions of the engine system shown in FIG. 6 are identical tothose of the engine system of FIG. 1, and thus, description thereof willnot be repeated.

DI delivery pipe 130 and PFI delivery pipe 160 are both subjected toheat of combustion of the fuel in the internal combustion engine. Here,DI delivery pipe 130 provided with in-cylinder injector 110 arranged inthe combustion chamber receives heat of a greater amount than PFIdelivery pipe 160.

Further, in engine 10, each cylinder 112 is provided with bothin-cylinder injector 110 and intake manifold injector 120. Thus, it isnecessary to carry out control of fuel injection ratio betweenin-cylinder injector 110 and intake manifold injector 120 for theoverall fuel injection quantity required having been calculatedaccording to vehicle operation states.

In principle, engine ECU 300 refers to a prepared map to set the fuelinjection ratio in accordance with the engine temperature and the engineoperation state (engine speed and load factor). Then, in accordance withthe fuel injection ratio thus set, fuel injection is carried out usingboth of in-cylinder injector 110 and intake manifold injector 120 orusing only in-cylinder injector 110 or intake manifold injector 120. Ina cold state of the engine, for example, the fuel injection ratio is setsuch that fuel injection is carried out using only intake manifoldinjector 120 from the standpoints of exhaust property and lubricationproperty, as described above.

Hereinafter, a configuration of the fuel supply system for an internalcombustion engine according to the second embodiment will be describedin detail with reference to FIG. 7.

Referring to FIG. 7, low-pressure fuel pump (feed pump) 180, fuel filter190, fuel tank 200, high-pressure fuel pump 155, and electromagneticspill valve (metering valve) 156 are included in the fuel supply system500 of FIG. 6.

Low-pressure fuel pump 180 of an electric motor-driven type dischargesthe fuel stored in fuel tank 200 at a prescribed pressure (lowpressure). The operation period and fuel discharge quantity (flow rate)of low-pressure fuel pump 180 are controlled based on a control signalfrom ECU 300#. ECU 300# corresponds to a functional part of engine ECU300 of FIG. 6 that is related to control of the fuel supply system.

The discharge side of low-pressure fuel pump 180 is connected to theintake side of high-pressure fuel pump 155 via fuel filter 190. Thedischarge side of high-pressure fuel pump 155 is connected to a fuelpipe 222 via a check valve 240 allowing flow directed to fuel pipe 222.Fuel pipe 222 is connected to the upstream side of DI delivery pipe 130that is formed as a tubular body provided with an arbitrary number ofin-cylinder injectors 110.

The discharge side of high-pressure fuel pump 155 is also connected tothe intake side of high-pressure fuel pump 155 via an electromagneticspill valve 156. High-pressure fuel pump 155 is of an engine driventype. With rotation of a pumping cam shaft driven by operation of engine10, for example, a plunger performs a reciprocating motion within acylinder, and thus, the fuel suctioned into a pressurizing chamber iscompressed and increased in pressure, and is discharged at a prescribedpressure (high pressure on the order of 12 MPa, for example). Theprescribed pressure (high pressure) is set to a level required foratomization of the fuel injected into the cylinder.

During the intake stroke where high-pressure fuel pump 155 suctions thefuel discharged from low-pressure fuel pump 180 into the pressurizingchamber, electromagnetic spill valve 156 is opened. During the discharge(pressurizing) stroke of high-pressure fuel pump 155, the fuelcompressed by the plunger in the pressurizing chamber is delivered tofuel pipe 222 while electromagnetic spill valve 156 is closed, and whileelectromagnetic spill valve 156 is open, the fuel within thepressurizing chamber flows back to the intake side of high-pressure fuelpump 155, with no fuel compressing operation being conducted.

With this configuration, it is possible to control the quantity of thefuel discharged from high-pressure fuel pump 155 by control ofopening/closing of electromagnetic spill valve 156 by ECU 300#. Thiseliminates the need for high-pressure fuel pump 155 to carry out theunnecessary fuel compressing operation exceeding the required overallfuel injection quantity, so that fuel efficiency in engine 10 serving asthe driving power source of high-pressure fuel pump 155 is improved.

DI delivery pipe 130 receives the fuel discharged from high-pressurefuel pump 155 via fuel pipe 222 on the upstream side, and delivers thefuel to an arbitrary number of in-cylinder injectors 110 for injectioninto the internal combustion engine (in-cylinder injection). Further, amechanical relief valve 250 is provided on the downstream side of DIdelivery pipe 130. Mechanical relief valve 250 opens when a pressureequal to or greater than a set pressure (high pressure on the order of12 MPa, for example) is applied, and guides the fuel within DI deliverypipe 130 to a connection pipe 224. As such, the fuel pressure within DIdelivery pipe 130 is maintained at a prescribed level.

The fuel sent out of DI delivery pipe 130 via connection pipe 224 issupplied to the upstream side of PFI delivery pipe 160. PFI deliverypipe 160 receives the fuel from connection pipe 224 on the upstreamside, and delivers the fuel to an arbitrary number of intake manifoldinjectors 120 for injection into the internal combustion engine (intakemanifold injection).

Further, a pressure regulator 260 is provided downstream of PFI deliverypipe 160 between the pipe 160 and a pressure release path 230. Pressureregulator 260 is configured to guide the fuel on the downstream side ofPFI delivery pipe 160 to pressure release path 230 when its fuelpressure becomes higher than a preset fuel pressure (low pressure on theorder of 400 kPa, for example). Thus, the fuel pressure within PFIdelivery pipe 160 is maintained at a prescribed pressure (low pressure)that is lower than the fuel pressure (high pressure) within DI deliverypipe 130. The fuel guided to pressure release path 230 is returned tofuel tank 200, for example.

The prescribed pressure (low pressure) may be set lower than thedischarge pressure (i.e., high pressure) of high-pressure fuel pump 155,since it only needs to be a level required for atomization of the fuelinjected into the intake manifold. By making the set fuel pressure inPFI delivery pipe 160 lower than that in DI delivery pipe 130, thedesigned withstand pressure of intake manifold injectors 120 and PFIdelivery pipe 160 not requiring fuel injection at high pressure can belowered, leading to reduction of manufacture cost.

As described above, in the fuel supply system according to the secondembodiment where DI delivery pipe 130 and PFI delivery pipe 160 areconnected in series, DI delivery pipe 130 for in-cylinder fuel injectionreceiving a relatively large amount of heat from the internal combustionengine is arranged upstream.

In this configuration, the fuel to be injected from intake manifoldinjectors 120 is supplied to PFI delivery pipe 160 after being passedthrough DI delivery pipe 130 that receives the large amount of heat.Thus, even in a cold state of the engine at the time of engine start orthe like, the temperature of the fuel within PFI delivery pipe 160, thatis, the temperature of the fuel injected from intake manifold injectors120, can be increased quickly. As a result, it is possible to downsizethe atomized particle size of the fuel injected from intake manifoldinjectors 120 in the cold state of the engine, thereby preventingdegradation of exhaust property.

Meanwhile, after combustion has proceeded in the internal combustionengine following the engine start, deposits may be produced due to thetemperature increase of in-cylinder injectors 110. In the fuel supplysystem of the present embodiment, the fuel to be injected from both ofin-cylinder injector 110 and intake manifold injector 120, that is, allthe fuel to be injected, is passed through DI delivery pipe 130, so thatit is possible to restrict the increase in temperature of the fuelwithin DI delivery pipe 130. This ensures the effect of coolingin-cylinder injector 110 by the fuel passed through DI delivery pipe130, or the fuel being injected therefrom. Accordingly, production ofdeposits can be prevented by restricting the increase in temperature atthe tip of in-cylinder injector 110.

In the fuel supply system shown in FIG. 7, low-pressure fuel pump 180and high-pressure fuel pump 155 each correspond to the “fuel pump” ofthe present invention, and PFI delivery pipe 160 and DI delivery pipe130 correspond to the “first fuel delivery pipe” and the “second fueldelivery pipe”, respectively, of the present invention. Further,mechanical relief valve 250 corresponds to the “first fuel pressureregulation means”, and pressure regulator 260 corresponds to the “secondfuel pressure regulation means” of the present invention.

In the fuel supply system according to the second embodiment, the fueldischarge quantity of high-pressure fuel pump 155 is relatively large,since it needs to discharge the fuel for both of in-cylinder injectionand intake manifold injection. For this reason, high-pressure fuel pump155 may have a simple configuration to compress all the suctioned fueland discharge the resultant fuel into fuel pipe 222, without provisionof the above-described electromagnetic spill valve 156 enablingadjustment of the discharge quantity.

Alternatively, as shown in FIG. 8, a relief valve 255 equipped with anelectromagnetic valve may be provided downstream of DI delivery pipe130, instead of mechanical relief valve 250.

Referring to FIG. 8, relief valve 255 functions in the same manner asmechanical relief valve 250 shown in FIG. 7 and, in addition, opens inresponse to an electromagnetic valve open instruction SV0 from ECU 300#so as to connect the downstream side of DI delivery pipe 130 as well asconnection pipe 224 (that is, the upstream side of PFI delivery pipe160) to pressure release path 230.

For example, at the time of stop of vehicle operation, when ECU 300#opens relief valve 255, the fuel pressure in DI delivery pipe 130 and inPFI delivery pipe 160 can be lowered sufficiently. This improves the oiltightness of in-cylinder injectors 110 and intake manifold injectors 120during the stop of vehicle operation, and thus, degradation in exhaustemission property at the next start of the engine due to the fuelleaking from these injectors can be suppressed.

Modification of Second Embodiment

A configuration of a fuel supply system according to a modification ofthe second embodiment of the present invention will now be explainedwith reference to FIG. 9.

Referring to FIG. 9, the fuel supply system according to themodification of the second embodiment differs from the fuel supplysystems shown in FIGS. 7 and 8 in that fuel pressure regulation means(mechanical relief valve 250 in FIG. 7 or relief valve 255 equipped withelectromagnetic valve in FIG. 8) is not provided downstream of DIdelivery pipe 130, and in that a mechanical relief valve 270 is providedbetween the downstream side of PFI delivery pipe 160 and pressurerelease path 230.

Mechanical relief valve 270 has the function similar to that ofmechanical relief valve 250 shown in FIG. 7. It opens when a pressureequal to or greater than a set pressure (high pressure on the order of12 MPa, for example) is applied, to guide the fuel within PFI deliverypipe 160 to pressure release path 230. That is, mechanical relief valve270 corresponds to the “fuel pressure regulation means” of the presentinvention.

Thus, in the fuel supply system shown in FIG. 9, the fuel pressure ofPFI delivery pipe 160 is set to a high pressure similarly to that of DIdelivery pipe 130. Thus, not only the fuel injection from in-cylinderinjectors 110, but also the fuel injection from intake manifoldinjectors 120 is carried out, at high pressure.

This can simplify the configuration of the system as compared with thefuel supply system of FIG. 7, since the fuel injection pressure fromboth injectors becomes the same. In addition, the atomized particle sizeof the fuel injected from intake manifold injectors 120 is furtherdownsized, and accordingly, exhaust emission property at the time ofintake manifold injection such as in the cold state of the engine canfurther be improved.

Alternatively, mechanical relief valve 270 provided downstream of PFIdelivery pipe 160 may be replaced with a relief valve 275 that opens inresponse to an electromagnetic valve open instruction SV0, as shown inFIG. 10.

Referring to FIG. 10, relief valve 275 functions in the same manner asmechanical relief valve 270, and additionally serves to connect thedownstream side of PFI delivery pipe 160 to pressure release path 230 inresponse to electromagnetic valve open instruction SV0 from ECU 300#.

When relief valve 275 is opened by the instruction from ECU 300# at thetime of stop of vehicle operation as in the case of electromagneticvalve-equipped relief valve 255, the fuel pressure in DI delivery pipe130 and in PFI delivery pipe 160 can be lowered sufficiently. Thisimproves oil tightness of in-cylinder injectors 110 and intake manifoldinjectors 120 during the stop of vehicle operation and, as a result,degradation in exhaust emission property at the next engine start due tothe fuel leaking from the injectors can be suppressed.

Third Embodiment

A third embodiment of the present invention will now be described withreference to FIGS. 11-14. In the third embodiment, it is assumed thatthe fuel supply system of the present invention is applied to an in-line4-cylinder engine.

FIG. 11 shows a cross-sectional structure of an engine 501 to which thefuel supply system of the present invention is applied.

Engine 501 is provided with a cylinder block 502 and a cylinder head503. A cylinder 521 is provided in cylinder block 502. A piston 522 iscontained in cylinder 521 in a reciprocable manner. A combustion chamber523 is formed in cylinder 521, which is surrounded by the innerperipheral surface of cylinder 521, the top face of piston 522 andcylinder head 503.

An intake pipe 531 and an exhaust pipe 532 are provided at cylinder head503. Intake pipe 531 is connected to combustion chamber 523 via anintake port 533. At intake port 533, an intake valve 535 is arranged,which opens/closes intake port 533 to change the connection statebetween intake pipe 531 and combustion chamber 523.

Exhaust pipe 532 is connected to combustion chamber 523 via an exhaustport 534. At exhaust port 534, an exhaust valve 536 is arranged, whichopens/closes exhaust port 534 to change the connection state betweenexhaust pipe 532 and combustion chamber 523.

Engine 501 is provided with a fuel supply system 505. Fuel supply system505 includes a fuel tank 551, an arbitrary number of in-cylinderinjectors DI and an arbitrary number of port injectors PI. The fuelwithin fuel tank 551 is supplied to in-cylinder injectors DI and portinjectors PI.

In-cylinder injector DI injects the fuel into combustion chamber 523.That is, in-cylinder injector DI is provided at cylinder head 503, withits injection hole arranged inside combustion chamber 523.

Port injector PI injects the fuel into intake port 533. That is, portinjector PI is provided at cylinder head 503, with its injection holearranged inside the intake manifold.

It is noted that engine 10 shown in FIGS. 1 and 6 has a cross-sectionalstructure similar to that of engine 501 in FIG. 11. That is, in-cylinderinjector DI and port injector PI of the third embodiment correspond toin-cylinder injector 110 and intake manifold injector 120, respectively,of the first and second embodiments.

FIG. 12 shows a structure of fuel supply system 505 of FIG. 11.

Firstly, the elements constituting the fuel supply system 505 will bedescribed.

A low-pressure fuel pump 552 pumps a fuel from a fuel tank 551 anddischarges the fuel to a high-pressure fuel pump 553. As low-pressurefuel pump 552, a fuel pump of an electric type discharging the fuel in aconstant quantity may be used.

High-pressure fuel pump 553 applies pressure to the fuel discharged fromlow-pressure fuel pump 552 and discharges the resultant fuel toinjectors DI, PI. As high-pressure fuel pump 553, a fuel pump of amechanical type applying pressure to the fuel by a reciprocating motionof a plunger via a camshaft may be used. In such high-pressure fuel pump553, the camshaft is driven via a crankshaft of engine 501.

The fuel discharge quantity of low-pressure fuel pump 552 is set suchthat the fuel of a sufficient quantity is supplied to high-pressure fuelpump 553 even when high-pressure fuel pump 553 is operating at themaximum rotational speed. An in-cylinder injection fuel delivery pipe554 supplies the fuel to in-cylinder injectors DI.

In-cylinder injectors DI are provided at in-cylinder injection fueldelivery pipe 554, and each inject the fuel into combustion chamber 523of the corresponding cylinder 521. A port injection fuel delivery pipe555 supplies the fuel to port injectors PI.

Port injectors PI are provided at port injection fuel delivery pipe 555,and each inject the fuel into intake port 533 of the correspondingcylinder 521.

An in-cylinder injection pressure regulation valve 556 regulates thepressure of the fuel within in-cylinder injection fuel delivery pipe 554not to exceed an in-cylinder injection pressure PA. This in-cylinderinjection pressure PA corresponds to the fuel pressure that is requiredto ensure accurate fuel injection via in-cylinder injectors DI.

A port injection pressure regulation valve 557 regulates the pressure ofthe fuel within port injection fuel delivery pipe 555 not to exceed aport injection pressure PB. This port injection pressure PB correspondsto the fuel pressure that is required to ensure accurate fuel injectionvia port injectors PI, which is set to a level lower than in-cylinderinjection pressure PA.

In the third embodiment, port injection fuel delivery pipe 555corresponds to the “intake manifold injection fuel delivery pipe” of thepresent invention, and port injection pressure regulation valve 557corresponds to the “intake manifold injection pressure regulation means”of the present invention.

Hereinafter, an operation manner of the in-cylinder injection pressureregulation valve will be described.

In-cylinder injection pressure regulation valve 556 includes an inletport 556A and an outlet port 556B, and also includes an open/close valvethat opens/closes a fuel passage (connecting the inlet port 556A and theoutlet port 556B) formed therein.

The open/close valve is normally held at a position closing the fuelpassage via a pressure regulation spring. When the pressure of the fuelon the inlet port 556A side (fuel within in-cylinder injection fueldelivery pipe 554) exceeds in-cylinder injection pressure PA, theopen/close valve moves to open the fuel passage, to cause the fuelwithin in-cylinder injection fuel delivery pipe 554 to flow out to thedownstream side of in-cylinder injection pressure regulation valve 556via outlet port 556B.

As the fuel flows out, when the pressure of the fuel on the inlet port556A side becomes equal to or lower than in-cylinder injection pressurePA, the open/close valve moves to close the fuel passage, so that theflow of the fuel from the inlet port 556A to outlet port 556B is shutoff.

As the opening/closing of the fuel passage by means of the open/closevalve is repeated in this manner, the pressure of the fuel inin-cylinder injection fuel delivery pipe 554 is controlled not to exceedin-cylinder injection pressure PA.

Next, an operation manner of the port injection pressure regulationvalve will be described.

Port injection pressure regulation valve 557 includes an inlet port 557Aand an outlet port 557B, and also includes an open/close valve thatopens/closes a fuel passage (connecting the inlet port 557A and theoutlet port 557B) formed therein.

The open/close valve is normally held at the position closing the fuelpassage via a pressure regulation spring. When the pressure of the fuelon the inlet port 557A side (fuel within port injection fuel deliverypipe 555) exceeds port injection pressure PB, the open/close valve movesto open the fuel passage, so that the fuel within port injection fueldelivery pipe 555 flows out to the downstream side of port injectionpressure regulation valve 557 via outlet port 557B.

As the fuel flows out, when the pressure of the fuel on the inlet port557A side becomes equal to or lower than port injection pressure PB, theopen/close valve moves to close the fuel passage, so that the flow ofthe fuel from inlet port 557A to outlet port 557B is shut off.

As the opening/closing of the fuel passage by means of the open/closevalve is repeated in this manner, the pressure of the fuel within portinjection fuel delivery pipe 555 is controlled not to exceed portinjection pressure PB.

In fuel supply system 505, the elements are connected through the fuelpipes as follows.

The discharge side of low-pressure fuel pump 552 is connected to theintake side of high-pressure fuel pump 553 via a first fuel pipe R1. Thedischarge side of high-pressure fuel pump 553 is connected to theupstream side of in-cylinder injection fuel delivery pipe 554 via asecond fuel pipe R2.

Inlet port 556A of in-cylinder injection pressure regulation valve 556is connected to second fuel pipe R2. Outlet port 556B of in-cylinderinjection pressure regulation valve 556 is connected to the upstreamside of port injection fuel delivery pipe 555 via a connection fuel pipeRE.

The downstream side of port injection fuel delivery pipe 555 isconnected to inlet port 557A of port injection pressure regulation valve557 via a third fuel pipe R3. Outlet port 557B of port injectionpressure regulation valve 557 is connected to fuel tank 551 via a fourthfuel pipe R4.

In the fuel supply system 505 of the third embodiment, first fuel pipeR1 and second fuel pipe R2 correspond to the “fuel supply pipe” of thepresent invention, and third fuel pipe R3 and fourth fuel pipe R4correspond to the “fuel return pipe” of the present invention.

FIG. 13 illustrates the flow of the fuel in fuel supply system 505during the operation of the engine.

The fuel within fuel tank 551 is discharged to first fuel pipe R1 vialow-pressure fuel pump 552. The fuel pressure within first fuel pipe R1is maintained not to exceed a discharge pressure (feed pressure PC) oflow-pressure fuel pump 552.

All of the fuel discharged from low-pressure fuel pump 552 is suppliedvia first fuel pipe R1 to high-pressure fuel pump 553.

The fuel supplied to high-pressure fuel pump 553 is applied withpressure by high-pressure fuel pump 553 to attain a pressure greaterthan feed pressure PC before being discharged to second fuel pipe R2.

The fuel discharged from high-pressure fuel pump 553 is supplied viasecond fuel pipe R2 to in-cylinder injection fuel delivery pipe 554. Thefuel pressure within in-cylinder injection fuel delivery pipe 554 (andin second fuel pipe R2) is maintained not to exceed in-cylinderinjection pressure PA by in-cylinder injection pressure regulation valve556.

The fuel flown out of outlet port 556B of in-cylinder injection pressureregulation valve 556 is supplied via connection fuel pipe RE to portinjection fuel delivery pipe 555. The fuel pressure within portinjection fuel delivery pipe 555 (and in connection fuel pipe RE) ismaintained not to exceed port injection pressure PB by port injectionpressure regulation valve 557.

The fuel flown out of outlet port 557B of port injection pressureregulation valve 557 is returned to fuel tank 551 via fourth fuel pipeR4. The fuel pressure within fourth fuel pipe R4 is maintained not toexceed a return pressure PD corresponding to the pressure within fueltank 551.

As explained in detail above, according to the fuel supply system for aninternal combustion engine of the third embodiment, the followingeffects are obtained.

(1) According to fuel supply system 505 of the third embodiment, all ofthe fuel discharged from low-pressure fuel pump 552 is supplied tohigh-pressure fuel pump 553. This advantageously suppresses occurrenceof vapor lock attributable to insufficient fuel supply from low-pressurefuel pump 552 to high-pressure fuel pump 553.

(2) According to fuel supply system 505 of the third embodiment, thepressure of the fuel within port injection fuel delivery pipe 555 isregulated by port injection pressure regulation valve 557. This ensuresaccurate fuel injection from port injectors PI.

(3) According to fuel supply system 505 of the third embodiment, thefuel path is branched at the downstream side of high-pressure fuel pump553 to the path for supplying the fuel to in-cylinder injection fueldelivery pipe 554 and the path for supplying the fuel to port injectionfuel delivery pipe 555. Thus, by only supplying the fuel tohigh-pressure fuel pump 553 in a quantity required at the maximumrotational speed of high-pressure fuel pump 553, occurrence of vaporlock attributable to insufficient fuel supply to high-pressure fuel pump553 can be avoided irrespective of the injection ratio betweenin-cylinder injectors DI and port injectors PI.

If the path for supplying the fuel to in-cylinder injection fueldelivery pipe 554 and the path for supplying the fuel to port injectionfuel delivery pipe 555 were branched at the upstream side ofhigh-pressure fuel pump 553, it would be necessary to set the dischargequantity of low-pressure fuel pump 552 taking account of the fuelinjection quantity from port injectors PI in addition to the fuelrequired at the maximum rotational speed of high-pressure fuel pump 553.That is, in order to avoid insufficient fuel supply to high-pressurefuel pump 553, the discharge quantity of low-pressure fuel pump 552would have to be set greater than in the case of the present embodiment.

According to fuel supply system 505 of the third embodiment, it isunnecessary to supply an excessive fuel through low-pressure fuel pump552, and thus, the discharge capability required for low-pressure fuelpump 552 can be made small.

Modification of Third Embodiment

A modification of the third embodiment of the present invention will nowbe described with reference to FIG. 14.

The fuel supply system of the modification of the third embodiment hasthe piping structure of the fuel supply system of the third embodimentmodified as follows.

FIG. 14 shows a structure of the fuel supply system 505# according tothe modification of the third embodiment. The fuel supply system of themodification of the third embodiment has the configuration similar tothat of the fuel supply system of the third embodiment except for thefollowing point.

In fuel supply system 505#, the downstream side of in-cylinder injectionfuel delivery pipe 554 is connected to inlet port 556A of in-cylinderinjection pressure regulation valve 556 via a fifth fuel pipe R5. Infuel supply system 505# of the modification of the third embodiment,first fuel pipe R1, second fuel pipe R2 and fifth fuel pipe R5correspond to the “fuel supply pipe” of the present invention.

According to the fuel supply system for an internal combustion engine ofthe modification of the third embodiment, the effects similar to thoseof (1) to (3) described above in the third embodiment can be obtained.

The following are the elements that can be modified in the thirdembodiment as well as in the modification thereof.

In the third embodiment and its modification, port injector PI forinjecting the fuel into intake port 533 has been provided. Port injectorPI may be replaced with any other injector, as long as it can serve asan intake manifold injector for injecting the fuel into an intakemanifold (including intake port, surge tank and the like).

Further, in the third embodiment and its modification, the presentinvention has been applied to a fuel supply system for an in-line4-cylinder engine. The present invention however is applicable to anyfuel supply system including an in-cylinder injector and an intakemanifold injector, to provide the similar effects.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

1. A fuel supply system for an internal combustion engine, comprising: afuel tank for storing a fuel; a first fuel pump actuated in response toan operation instruction associated with an operation period of saidinternal combustion engine and for discharging the fuel in said fueltank at a first pressure; a first fuel delivery pipe formed as a tubularbody having first fuel injection means and for receiving the fueldischarged from said first fuel pump at an upstream side and deliveringthe fuel to said first fuel injection means such that the fuel isinjected into said internal combustion engine; a second fuel pumpconnected in series with said first fuel delivery pipe, actuated duringoperation of said internal combustion engine, and for applying pressureto the fuel received from a downstream side of said first fuel deliverypipe to discharge the fuel at a second pressure; a second fuel deliverypipe formed as a tubular body and connected in series with said firstdelivery pipe, said second pipe having a second fuel injection means andfor receiving the fuel discharged from said second fuel pump at anupstream side and delivering the fuel to said second fuel injectionmeans such that the fuel is injected into said internal combustionengine; a pressure regulation unit provided on a fuel path between saidfirst fuel delivery pipe and said second fuel pump and for guiding thefuel in the fuel path to a pressure release path when a pressure of thefuel in the fuel path exceeds said first pressure; and pressure releasemeans provided between the fuel path downstream of said second fuel pumpand said pressure release path, actuated at the stop of operation of avehicle, and for guiding the fuel in the fuel path to said pressurerelease path.
 2. The fuel supply system for an internal combustionengine according to claim 1, wherein said pressure release path is afuel return pipe to said fuel tank.
 3. The fuel supply system for aninternal combustion engine according to claim 1, wherein said first fuelinjection means injects the fuel into an intake manifold of saidinternal combustion engine, and said second fuel injection means injectsthe fuel into a combustion chamber of said internal combustion engine.4. A fuel supply system for an internal combustion engine, comprising: afuel tank for storing a fuel; a first fuel pump actuated in response toan operation instruction associated with an operation period of saidinternal combustion engine and for discharging the fuel in said fueltank at a first pressure; a first fuel delivery pipe formed as a tubularbody having first fuel injection means and for receiving the fueldischarged from said first fuel pump at an upstream side and deliveringthe fuel to said first fuel injection means such that the fuel isinjected into said internal combustion engine; a pressure regulationunit provided on a fuel path between said first fuel pump and anupstream side of said first fuel delivery pipe and for guiding the fuelin the fuel path to a pressure release path when a pressure of the fuelin the fuel path exceeds said first pressure; a second fuel pumpactuated during operation of said internal combustion engine and forreceiving the fuel output from said first fuel pump and further applyingpressure to the fuel to discharge the fuel at a second pressure; asecond fuel delivery pipe formed as a tubular body having a second fuelinjection means and for receiving the fuel discharged from said secondfuel pump and delivering the fuel to said second fuel injection meanssuch that the fuel is injected into said internal combustion engine;first pressure release means provided on a fuel path between saidpressure regulation unit and said first fuel delivery pipe, activated atthe stop of operation of a vehicle and for guiding the fuel in the fuelpath to a pressure release path; and second pressure release meansprovided on a fuel path downstream of said second fuel pump, activatedat the stop of the operation of the vehicle and for guiding the fuel inthe fuel path to a pressure release path.
 5. The fuel supply system foran internal combustion engine according to claim 4, wherein saidpressure regulation unit is integrally provided in said fuel tank. 6.The fuel supply system for an internal combustion engine according toclaim 4, wherein said pressure release path is a fuel return pipe tosaid fuel tank.
 7. The fuel supply system for an internal combustionengine according to claim 4, wherein said first fuel injection meansinjects the fuel into an intake manifold of said internal combustionengine, and said second fuel injection means injects the fuel into acombustion chamber of said internal combustion engine.
 8. A fuel supplysystem for an internal combustion engine, comprising: a fuel tank forstoring a fuel; a first fuel pump actuated in response to an operationinstruction associated with an operation period of said internalcombustion engine and for discharging the fuel in said fuel tank at afirst pressure; a first fuel delivery pipe formed as a tubular bodyhaving a first fuel injection unit and configured to receive the fueldischarged from said first fuel pump at an upstream side and deliver thefuel to said first fuel injection unit such that the fuel is injectedinto said internal combustion engine; a second fuel pump connected inseries with said first fuel delivery pipe, actuated during operation ofsaid internal combustion engine, and configured to apply pressure to thefuel received from a downstream side of said first fuel delivery pipe todischarge the fuel at a second pressure; a second fuel delivery pipeformed as a tubular body and connected in series with said firstdelivery pipe, said second pipe having a second fuel injection unit andconfigured to receive the fuel discharged from said second fuel pump atan upstream side and deliver the fuel to said second fuel injection unitsuch that the fuel is injected into said internal combustion engine; apressure regulation unit provided on a fuel path between said first fueldelivery pipe and said second fuel pump and configured to guide the fuelin the fuel path to a pressure release path when a pressure of the fuelin the fuel path exceeds said first pressure; and a pressure releaseunit provided between the fuel path downstream of said second fuel pumpand said pressure release path, actuated at the stop of operation of avehicle, and configured to guide the fuel in the fuel path to saidpressure release path.
 9. The fuel supply system for an internalcombustion engine according to claim 8, wherein said pressure releasepath is a fuel return pipe to said fuel tank.
 10. The fuel supply systemfor an internal combustion engine according to claim 8, wherein saidfirst fuel injection unit is configured to inject the fuel into anintake manifold of said internal combustion engine, and said second fuelinjection unit is configured to inject the fuel into a combustionchamber of said internal combustion engine.
 11. A fuel supply system foran internal combustion engine, comprising: a fuel tank for storing afuel; a first fuel pump actuated in response to an operation instructionassociated with an operation period of said internal combustion engineand for discharging the fuel in said fuel tank at a first pressure; afirst fuel delivery pipe formed as a tubular body having a first fuelinjection unit and configured to receive the fuel discharged from saidfirst fuel pump at an upstream side and deliver the fuel to said firstfuel injection unit such that the fuel is injected into said internalcombustion engine; a pressure regulation unit provided on a fuel pathbetween said first fuel pump and an upstream side of said first fueldelivery pipe and configured to guide the fuel in the fuel path to apressure release path when a pressure of the fuel in the fuel pathexceeds said first pressure; a second fuel pump actuated duringoperation of said internal combustion engine and configured to receivethe fuel output from said first fuel pump and further apply pressure tothe fuel to discharge the fuel at a second pressure; a second fueldelivery pipe formed as a tubular body having a second fuel injectionunit and configured to receive the fuel discharged from said second fuelpump and deliver the fuel to said second fuel injection unit such thatthe fuel is injected into said internal combustion engine; a firstpressure release unit provided on a fuel path between said pressureregulation unit and said first fuel delivery pipe, activated at the stopof operation of a vehicle and configured to guide the fuel in the fuelpath to a pressure release path; and a second pressure release unitprovided on a fuel path downstream of said second fuel pump, activatedat the stop of the operation of the vehicle and configured to guide thefuel in the fuel path to a pressure release path.
 12. The fuel supplysystem for an internal combustion engine according to claim 11, whereinsaid pressure regulation unit is integrally provided in said fuel tank.13. The fuel supply system for an internal combustion engine accordingto claim 11, wherein said pressure release path is a fuel return pipe tosaid fuel tank.
 14. The fuel supply system for an internal combustionengine according to claim 11, wherein said first fuel injection unit isconfigured to inject the fuel into an intake manifold of said internalcombustion engine, and said second fuel injection unit is configured toinject the fuel into a combustion chamber of said internal combustionengine.